1. Field of the Invention
The present invention relates to an image forming apparatus comprising control means employing a fuzzy inference.
2. Description of the Related Art
Hitherto, in a control device of an image forming apparatus of the type described above, a control is performed in accordance with a rule on a definite judgement made in accordance with the quantity of state.
For example, a fixing device is usually arranged in such a manner that the temperature of the fixing device is detected by a temperature sensing device such as a thermistor and a heat source such as a heater is controlled with reference to a predetermined temperature level. For example, if the detected temperature is lower than 180.degree. C., the heater is turned on, while the heater is turned off if the detected temperature is higher than 180.degree. C.
In order to reduce the undesirable change with respect to a desired temperature, a variety of means have been proposed, for example, the time interval or duration in which the heater is turned on is controlled to be changed in accordance with the present temperature.
However, an image forming apparatus such as a copying machine suffers from an excessive change due to the environmental conditions and the relationship between the quantity of state of which and the control quantity of which is mainly controlled by a fuzzy relationship. Therefore, if the number of the quantities of states increases, it is very difficult to control in accordance with a predetermined rule.
For example, in a temperature control of a fixing device, it has been experientially known that the performance of fixing toner transferred to transfer paper is complexly changed if the quantity of state, such as room temperature, the number of sheets to be copied, the density of the original, the type of paper, and the temperature of the fixing device, has been changed. However, it has been very difficult to make a rule about the relationship between the quantity of state of the type described above and the control quantity. Specifically, the degree of heat radiation becomes different depending upon the circumferential conditions and the state whether or not the paper is being conveyed. Therefore, the conventional control, which is arranged in such a manner that the heat control device thereof is turned on when the temperature has exceeded a predetermined temperature level and the same is turned off when the temperature has been lowered below the above-described level, causes undesirable change due to the temperature (to be called "temperature ripple" hereinafter) to be generated. It is necessary for the minimum value of the above-described temperature ripple to be a temperature level at which toner can be satisfactorily fixed on to the transfer paper. Therefore, the temperature set for the heat control device must be higher, by a considerably degree, than the ideal state. Therefore, problems arise in that exceeding power is necessary and the materials for forming the fixing device must have satisfactory heat resistance.
A fixing device for a copying machine or a laser beam printer, and, in particular, a fixing device, which comprises a pair of rotary bodies having a fixing roller and a pressure application roller are rotated during the warming up operation of the device, are usually arranged in such a manner that the temperature of the fixing roller is detected by a temperature sensing device such as a thermistor and a heat source such as a heater is controlled with reference to a predetermined temperature level.
A problem arises in that the fixing performance deteriorates since the pressure application roller has not be sufficiently heated immediately after the temperature of the fixing roller has reached the set temperature at which the warming up operation is ended after the power supply.
Therefore, the pressure application roller is heated by rotating the pair of the rollers during the warming up multiple operations (to be called "multiple previous rotations" hereinafter).
The multiple previous rotations have been usually conducted in accordance with the surface temperature of the fixing roller.
However, since the fixing performance depends upon the temperature of the recording paper passing through the fixing device and the water content of the same, a stable fixing characteristics cannot be obtained by the above-described method.
Furthermore, a problem arises in that the copy restarting time after a jam has been eliminated becomes delayed if the multiple previous rotations are uniformly conducted although the pressure application roller has been sufficiently heated up in a case where the operation of the copying machine is stopped due to the jam.
A fact has been experientially known that the fixing performance becomes different depending upon the temperature of the pressure applying roller and that of transfer paper although the temperature of the fixing roller has reached the predetermined level. However the relationship between the quantity of state and the control quantity cannot be regulated.
Hitherto, in order to prevent the deterioration in the fixing performance, a multiplicity of structures have been proposed, for example, in Japanese Patent Laid-Open No. 56-25754 in which the fixing roller is rotated at low speed when the temperature of the fixing roller is lower than a predetermined level while the same is rotated at high speed when the temperature of it is higher than the predetermined level. Another structure has been disclosed in Japanese Patent Laid-Open No. 56-85770 in which the copying interval is changed in accordance with the type of the subject whether the subject to be copied is a line image or an area image. Furthermore, a structure has been disclosed in Japanese Patent Laid-Open No. 56-154757 in which the number of sheets to be copied per unit time period is changed by the thermal capacity. In addition, another structure has been proposed in which the number of sheets to be copied per unit time period is changed depending upon the ambient temperature.
However, according to each of the above-described conventional structures, the copying speed or the paper feeding interval has been determined by an excessive switching between low temperature and high temperature or in accordance with the insufficient number of the quantities of states. However, since the fixing performance is actually influenced by a multiplicity of factors, it is necessary to properly determine the desired fixing temperature and the copying interval on the basis of a multiplicity of quantities of states as an alternative to a sole quantity of state such as the ambient temperature. However, it has been very difficult to properly control the multiplicity of the quantities of states.
Another type image forming apparatus, that is, an ink jet recording apparatus has been known in which ink is discharged toward recording paper so as to form dots on the recording paper, whereby characters and/or images can be formed by the dots. The recording head employed in the above-described ink jet recording apparatus is able to perform a high quality image recording since the discharge port thereof can be structured precisely. Some of the above-described ink jet recording apparatus employ an ink discharge method arranged in such a manner that ink is discharged by the effect of pressure. The above-described pressure discharge method is exemplified by a method in which ink is supplied with pressure by an electromechanical conversion device such as the piezo electric device and a method in which bubbles are generated in the ink by heat generated by the electrothermal conversion device and the bubbles are enlarged to create pressure in the ink.
FIG. 10 illustrates a recording head which employs an electrothermal conversion device of the type described above as the pressure application means.
FIG. 10 is a perspective view which schematically illustrates the structure of an ink jet recording head of the type described above. Referring to the drawing, an electrothermal conversion member 103, an electrode 104, a liquid passage wall 105 are formed on a substrate 102 made of Si or the like by an etching, an evaporation and a spattering processes which are similar to those for manufacturing a semiconductor device. Then, a top board 106 is fastened to the above-described elements so that a recording head 101 is constituted. Ink 112 is supplied to a common liquid chamber 108 of the recording head 101 from a liquid reservoir (omitted from illustration), for example, an ink tank via a supply pipe 107. Referring to the drawing, reference numeral 109 represents a connector for the ink supply pipe 107. The ink 112 supplied to the common liquid chamber 108 is, due to capillary force or a pressure change taken place when ink is discharged, supplied to a liquid passage 110. The ink 112 can be stably held by forming a meniscus at the opening of the front portion of the liquid passage 110, that is in the vicinity of a discharge port. When an extremely short electric pulse is applied to the electrothermal conversion member 103, the ink 112 on the electrothermal conversion member 103 is heated, causing a film boiling. As a result of this film boiling, bubbles are enlarged and ink 112 is thereby discharged.
The thus structured recording head can be arranged in such a manner that, in particular, the discharge ports are precisely provided at high density. Therefore, it is able to perform an excellent recording exhibiting a high resolution. Therefore, it has attracted attention recently.
However, the ink jet recording apparatus arises a variety of problems due to its arrangement in which ink is used as the recording agent. For example, a problem arises in that dew condensation takes place at the discharge port of the recording head due to the difference between the temperature of ink and the ambient temperature. Another problem arises in that ink droplet, generated from ink mist formed at the time of discharging ink, adheres to the discharge port. That is, water droplet adhered to the discharge port influences the ink discharge, causing the discharge direction to be deviated, and what is even worse, ink cannot be discharged. Furthermore, dust such as paper dust separated from recording paper and floating in the atmosphere can be adhered to the discharge port which has been wetted by the water droplets. As a result, the ink discharge cannot be smoothly conducted, and what is worse ink cannot be discharged. The water droplets or dust critically influences the recording head of the type in which the discharge ports are precisely provided with high density.
In order to overcome the above-described problem arisen in that the ink cannot be smoothly discharged or ink cannot be discharged, a variety of structures for stabilizing the discharge by removing water droplets and dust have been disclosed. For example, a structure has been disclosed in which the discharge port is wiped by a flexible blade made of plastic or rubber so as to remove dust or the like. Another structure has been disclosed in which a removal member comprising an ink absorbing material such as a porous member is brought into contact with the discharge port so as to remove water droplets or dust by absorbing them. Some of the above-described structures employ a structure in which ink is leaked by a pressure application means through the discharge port so as to absorb water droplets and dust so that the dust and/or water droplets can be satisfactorily absorbed by the removal member.
However, the discharge stabilizing operation for removing dust or the like must be conducted at a predetermined interval during the recording operation performed by the ink jet recording apparatus or conducted if it is desired. In this case, the time taken to complete the above-described operation lowers the recording speed of the recording apparatus.
Therefore, a variety of attempts have been made so as to prevent the deterioration in the recording speed by elongating the interval of the removal operations by controlling the timing of this operation in accordance with the continuous recording time period counted by, for example, a timer, the ambient temperature or humidity detected by a sensor and the discharge duty at the discharge port, that is, the recording pixel density or the like.
However, in the above-described control of the timing of performing the removal operation, it is very difficult to obtain a quantitative relationship between the quantity (to be called "the quantity of state" hereinafter) which becomes an action factor for causing the water droplets or dust to be adhered such as the continuous recording time period, the ambient temperature and humidity and discharge duty and the interval (time) (to be called "the control quantity" hereinafter) which is the factor to be controlled. In the case where a plurality of the quantity of states are related to one another, another problem arises in that the relationship between these quantities of states and the control quantity cannot be easily obtained. Even if the relationship can be obtained, the necessary calculations become too complicated.
Hitherto, in the control of the interval of the discharge stabilizing operation, the control quantity with respect to the quantities of states, that is, the interval cannot be determined in the most suitable manner. Therefore, unnecessary long time takes place in the conventional apparatus for the purpose of removing water droplets and/or dust. Therefore, the recording speed of the apparatus is lowered unsatisfactorily.